Abstract: This study examines the typhoon In-fa in 2021 to investigate the impact of initial errors at different scales on the forecast of tropical cyclone track and intensity. The WRF model was driven separately by the FNL (Final Reanalysis Data) from NCEP and the ERA5 (the fifth major global reanalysis data) from ECMWF to conduct long-term (14 days) and high-resolution (3 km) simulations of typhoon In-Fa. These two simulations generated the control experiments CTL_F and CTL_E, respectively. The simulation results of experiments CTL_F and CTL_E were then compared against the best track, with the one closer to the best track regarded as the true value and the other as the forecast with errors. The differences of the initial fields of CTL_F and CTL_E was decomposed into small scale (＜200 km), mesoscale (200～2000 km), and large scale (＞2000 km) field. By superimposing these errors with three scales onto the true initial field and comparing the following simulations, the study examines the impact of errors at different scales on the simulated forecast of tropical cyclones, and analyzes the relative contributions of each scale of error to the forecasts. The results indicate that mesoscale errors have the decisive impact on forecasts during the first 10 days, both in terms of track and intensity. Over the subsequent 4 days, the contributions from large-scale and small-scale errors became more significant, with the effects of the three scale errors becoming comparable. In addition, mesoscale errors in the early stage shifted the typhoon track eastward and intensified its strength, while large and small-scale errors caused the typhoon track to shift westward and weakened the typhoon. Analysis reveals that the majority of error information is reflected in mesoscale error, making its role particularly significant in the early stages. Mesoscale errors slightly accelerate the speed of typhoon intensification and significantly slow down the speed of typhoon attenuation, while large-scale and small-scale errors slightly slow down the speed of typhoon intensification and significantly accelerate the speed of typhoon attenuation. Furthermore, the superimposed mesoscale error enhances the initial strength of the cyclone, resulting in an eastward track and later landfall. Therefore, mesoscale error leads to a stronger typhoon intensity. Conversely, large- and small-scale errors drive the track westward, causing an earlier landfall and reducing the typhoon’s overall strength.